In the manufacture of semiconductor chips, as is well known among people skilled in the art, a plurality of rectangular regions are defined on the face of a semiconductor wafer by streets arranged in a lattice pattern, and a semiconductor circuit is formed in each of the rectangular regions. This semiconductor wafer is cut along the streets to separate the rectangular regions individually, thereby forming semiconductor chips. For cutting along the streets, a machining device called a dicer is usually used. Such a machining device comprises workpiece holding means for holding a workpiece, namely, a semiconductor wafer, cutting means for cutting the semiconductor wafer held by the workpiece holding means, and moving means for moving the workpiece holding means and the cutting means relative to each other. The cutting means includes a rotatably mounted spindle, a cutting blade mounted on the spindle, and a rotational drive source for rotating the spindle. As the cutting blade, there is advantageously used a thin disk-shaped blade, called a diamond blade, which can be formed by binding diamond grains with a nickel plating or a suitable bond, such as a resin bond.
In recent times, a semiconductor wafer having a low dielectric constant insulator laminated on the face of a semiconductor wafer body, such as a silicon wafer, has been put to practical use. Examples of the low dielectric constant insulator are films of materials having a lower dielectric constant (e.g., dielectric constant k=about 2.5 to 3.6) than that of an SiO2 film (k=about 4.1), for example, a film of an inorganic material such as SiOF, BSG (SiOB) or H-containing polysiloxane (HSQ), a film of an organic material, such as a polyimide-based or parylene-based or polytetrafluoroethylene-based polymer film, and a porous silica film comprising methyl-containing polysiloxane or the like. Assume that such a semiconductor wafer is cut with the aforementioned machining device called a dicer, that is, cut by the action of the cutting blade called a diamond blade. In this case, there is a tendency toward the occurrence of the impermissible event that a surface layer, i.e. a low dielectric constant insulator layer, peels off the semiconductor wafer body even in regions adjacent to the streets, owing to the marked brittleness of the low dielectric constant insulator. Thus, before cutting of the semiconductor wafer by the machining device called a dicer, it is attempted to remove the low dielectric constant insulator by shining a laser beam to the streets.
However, when a laser beam is shone to the semiconductor wafer as the workpiece, thereby removing the low dielectric constant insulator, the following problem has been found to occur: Melt refuse (i.e. debris) from the low dielectric constant insulator, which is formed by shining of the laser beam, scatters and adheres to the surface of the rectangular region of the semiconductor wafer. As a result, the semiconductor circuit tends to be contaminated.